Israel and the United States strongly criticized Russia over its decision to transfer the advanced S-300 surface-to-air missile system to Syria.

Russian President Vladimir Putin told Israeli Prime Minister Benjamin Netanyahu of Moscow’s decision to supply Syria with the system.

According to the Prime Minister’s Office, Netanyahu told Putin that “transferring advanced weapons systems into irresponsible hands will increase the dangers in the region, and added that Israel will continue to defend its security and its interests.”

U.S. National Security Advisor John Bolton also called Russia’s decision a “major mistake,” and it would cause “significant escalation” in tensions.

The decision by Moscow comes amid the fallout over the downing of a Russian military jet in Syria last week. Syrian air defenses fired on Israeli jet that had been operating in the area, but instead hit the Russia spy plane, killing 15 soldiers.

Earlier this year, Russia reportedly considered supplying the Syrian government with the S-300 system. However, that move was later retracted following a visit by Netanyahu to Moscow in May.

Russian Defense Minister Sergei Shoigu said that while Moscow had in the past obliged Israel in refraining from transferring the system, last week’s crash forced the country to take “adequate retaliatory measures” to maintain their safety.

“A modern S-300 air-defense missile system will be transferred to the Syrian armed forces within two weeks,” he said, according to Reuters. The system will “significantly increase the Syrian army’s combat capabilities,” he said.

The S-300 surface-to-air-missile was initially developed under the Soviet Union. Its newer variants are regarded as the one of the more effective anti-aircraft missile systems in the world.